Charge: definition in chemistry
Charge: A property of matter that causes electrical attraction or repulsion. Protons carry a positive charge and electrons an equal negative charge.
Opposite charges attract and like charges repel, and these forces hold atoms, ions and many compounds together. Charge is measured in coulombs, but chemists usually count it in units of the elementary charge, so a proton is +1 and an electron is −1. An atom with equal numbers of protons and electrons is neutral; gaining or losing electrons gives it a charge and turns it into an ion.
Examples
- Na⁺ — a sodium ion with a charge of +1
- Cl⁻ — a chloride ion with a charge of −1
- O²⁻ — an oxide ion with a charge of −2
- Al³⁺ — an aluminum ion with a charge of +3
On the periodic table
Common ion charges follow the groups: group 1 metals form +1 ions, group 2 form +2, group 16 nonmetals form −2 and group 17 form −1.